1. Field of the Invention
The present invention relates to a method and system for the onboard storage of a large volume of high-pressure hydrogen or natural gas on vehicles powered by either internal combustion engines or fuel cells. Particularly, this invention relates to a rear suspension subassembly having improved structural rigidity, that is designed to straddle a large diameter high-pressure storage tank with high volumetric efficiency.
2. Description of the Relation Art
Hydrogen powered Fuel Cell Vehicles (FCV) and natural gas powered vehicles are solution to problems of air quality and dependency on petroleum fuel. Fuel cells produce electricity by combining hydrogen with oxygen from air to produce electrical power and give off only water vapor. Natural gas fueled internal combustion engine vehicles produce exhaust emissions that are a fraction of diesel or gasoline fueled counterparts. The onboard vehicle storage of hydrogen gas or natural gas poses challenges in the areas of relatively low energy density, system cost, crashworthiness, and vehicle packaging. Gaseous fuels (e.g., hydrogen and natural gas), stored at high pressure, carry a fraction (between ⅓rd and ⅛th) of the energy density compared to gasoline or diesel fuels. To have an acceptable driving range, significant container volume is needed. Furthermore high-pressure tanks are most efficiently built as cylinders, with large diameter cylinders offering high volumetric efficiencies and manufacturing cost advantages needed for practical and affordable gaseous fuel vehicles. Large cylinders however pose a problem for vehicle packaging, impacting vehicle interior space (passenger, trunk or truckbed), undercarriage clearance and/or room for suspension assemblies that provide handling and ride acceptable to drivers. To support crashworthiness the storage tank needs to be placed as far as possible from the back of the vehicle for structural protection. In designing a suspension system that straddles a large diameter tank full consideration of the functions of the suspension system must be taken into account. The purpose of the suspension system is to (1) support the weight of the vehicle, (2) cushion bumps and holes on the road, (3) maintain traction between the tires and the road and (4) hold the wheels in alignment.
The suspension assembly includes springs, dampers, linkages and tires that control the way in which a vehicle moves and reacts to roadway disturbances and directional changes.
The angular and vertical movements of the wheels provide directional control compensating for (or utilize) body roll to improve cornering and respond to roadway irregularities in order to smooth out the ride and maintain adhesion. Wheels are connected to the sprung mass (car body) through linkages and are therefore affected by the rolling and pitching movements that occur about the suspensions system's reaction centers. It is critical that the suspension linkages be designed to allow the wheels to meet the dynamic requirements of various combinations of events. However, the designer is constrained by mechanical conflicts between structural members, and fuel storage containers that also must fit into the vehicle.
A large-volume gaseous fuel tank, mounted between the rear wheels provides suspension design and structural difficulties. As a result, the rear suspension may not be sufficiently stiff to keep the rear wheels aligned, which leads to the vehicle's lateral instability, particularly when it is driven on rough terrain. To minimize the lateral instability, the rear suspension has to be designed to exhibit enhanced stiffness or rigidity to minimize the negative effect produced by the road irregularities on the wheels.
U.S. Pat. Nos. 5,924,734 and 6,086,103 disclose a rear suspension flanking a fuel tank assembly and attached to the front portion of the vehicle by means of front ends of opposite trailing (control) arms in front of the fuel tank assembly. Accordingly, the rear suspension has only two reaction points aligned with one another and spaced frontward from the wheel axis. This structure may not be rigid enough to provide stiffness sufficient to keep the rear wheels aligned. Misalignment of the rear wheels leading to the lateral instability of the car renders the ride both unpleasant and unsafe. In addition stabilizing arms aligned with the principal axis of the storage tank and the wheel occupy valuable space in the undercarriage that reduces the overall tank length and thus the volume of gaseous fuel that can be carried onboard.
It is desirable to increase stiffness of a rear suspension while providing for a large open space between the wheels, unencumbered by stiffening arms in order to house a longer tank and thus a large volume of compressed gas fuel.